St Olaf's Church in Tallinn

St Olaf's Church in Tallinn, the city's biggest medieval structure, took its name from the sainted Norwegian king Olav II Haraldsson. The church was first mentioned in 1267. It became one of the main churches in the Lower Town and formed its own congregation, which at first mostly comprised Scandinavian merchants and craftsmen and few Estonians.

The evangelical preachings of the then chaplain of the church, Zacharias Hasse, led to the start of the reformation in Tallinn in 1523.